Semiconductor device

ABSTRACT

A semiconductor device includes a semiconductor substrate including a main surface; a plurality of first interconnections formed in a capacitance forming region defined on the main surface and extending in a predetermined direction; a plurality of second interconnections each adjacent to the first interconnection located at an edge of the capacitance forming region, extending in the predetermined direction, and having a fixed potential; and an insulating layer formed on the main surface and filling in between each of the first interconnections and between the first interconnection and the second interconnection adjacent to each other. The first interconnections and the second interconnections are located at substantially equal intervals in a plane parallel to the main surface, and located to align in a direction substantially perpendicular to the predetermined direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and moreparticularly, to a semiconductor device having a capacitive elementutilizing an interconnection layer.

2. Description of the Background Art

Recently, capacitive elements utilizing a parasitic capacitance betweeninterconnections have started to be used along with processminiaturization. A semiconductor integrated circuit device having such acapacitive element is disclosed for example in Japanese PatentLaying-Open No. 2001-177056. The semiconductor integrated circuit devicedisclosed in Japanese Patent Laying-Open No. 2001-177056 includes afirst electrode, a second electrode, and a dielectric film sandwichedbetween the first and the second electrodes, constituting a capacitiveelement. The first electrodes and the second electrodes are arranged toface each other in a plane direction and a thickness direction of asemiconductor substrate.

Japanese Patent Laying-Open No. 2002-100732 discloses a method offorming a capacitive element in which at least two interconnectionsformed in an identical interconnection layer are arranged in proximityto each other to obtain an interconnection capacitance serving as acapacitive element.

Further, Japanese Patent Laying-Open No. 2003-152085 discloses asemiconductor device for preventing noise coupling to an MIM(Metal-Insulator-Metal) capacitance and a method of manufacturing thesame. The semiconductor device disclosed in Japanese Patent Laying-OpenNo. 2003-152085 includes a semiconductor substrate, a capacitive elementformed above the semiconductor substrate, and at least a shield layerformed above or below the capacitive element. In another semiconductordevice, a stacked film electrically connected to the shield layer isformed in the same layer as the capacitive element to cause the stackedfilm to operate similarly to the shield layer.

Furthermore, a capacitive element utilizing an interlayer capacitancebetween interconnection layers is disclosed in “Capacity Limits andMatching Properties of Integrated Capacitors” by Robert Aparicio et al.,IEEE Journal of Solid-state Circuits, Vol. 37, No. 3, March 2002, pp.384-393.

However, the semiconductor integrated circuit device disclosed inJapanese Patent Laying-Open No. 2001-177056 and the method of forming acapacitive element disclosed in Japanese Patent Laying-Open No.2002-100732 do not include a measure to reduce interference with thecapacitive element by an external circuit. Consequently, there arises aproblem that the capacitance of the capacitive element fluctuates.Particularly, as an external circuit such as a digital portionprogresses to operate faster, the measure against such a problem isincreasingly required.

Further, in the semiconductor integrated circuit device or the likedisclosed in Japanese Patent Laying-Open Nos. 2001-177056, 2002-100732and 2003-152085, if interconnection layers and silicon gate layers arearranged with uneven density, the unevenness will cause a difference inthe progress of etching. Thus, the configuration obtained at the end ofthe process may have a non-uniform finish. Furthermore, if an activeregion and the like formed in a main surface of the semiconductorsubstrate does not have an area satisfying a predetermined ratio to afixed region on the main surface, it is not possible to form a layeruniformly over the main surface. Thus, it becomes difficult to controletching appropriately when forming a capacitive element on the film. Forthese reasons, it is not possible to form a capacitive element offeringa desired characteristic.

SUMMARY OF THE INVENTION

To solve the problems described above, an object of the presentinvention is to provide a semiconductor device having a capacitiveelement for which external electrical interference is sufficientlyreduced and offering a desired characteristic.

The semiconductor device according to the present invention includes asemiconductor substrate including a main surface; a plurality of firstinterconnections formed in a capacitance forming region defined on themain surface and extending in a predetermined direction; a plurality ofsecond interconnections each adjacent to one of the firstinterconnections located at an edge of the capacitance forming region,extending in the predetermined direction, and having a fixed potential;and an insulating layer formed on the main surface and filling inbetween each of the plurality of first interconnections and between thefirst interconnection and the second interconnection adjacent to eachother. The plurality of first interconnections and the plurality ofsecond interconnections are located at substantially equal intervals ina first plane parallel to the main surface, and located to align in adirection substantially perpendicular to the predetermined direction.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device in a firstembodiment of the present invention.

FIG. 2 is a plan view of the semiconductor device taken along thearrowed line II-II in FIG. 1.

FIG. 3 is a cross-sectional view taken along the line III-II in FIG. 2.

FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 2.

FIG. 5 is a cross-sectional view showing a semiconductor device in asecond embodiment of the present invention.

FIG. 6 is a plan view of the semiconductor device taken along thearrowed line VI-VI in FIG. 5.

FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6.

FIG. 8 is a cross-sectional view showing a semiconductor device in athird embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a semiconductor device in afourth embodiment of the present invention.

FIG. 10 is a plan view of the semiconductor device taken along thearrowed line X-X in FIG. 9.

FIG. 11 is a cross-sectional view taken along the line XI-XI in FIG. 10.

FIG. 12 is a cross-sectional view taken along the line XII-XII in FIG.10.

FIGS. 13 to 22 are cross-sectional views showing semiconductor devicesin fifth to fourteenth embodiments of the present invention,respectively.

FIG. 23 is a plan view of the semiconductor device taken along thearrowed line XXIII-XXIII in FIG. 22.

FIGS. 24 and 25 are cross-sectional views showing semiconductor devicesin fifteenth and sixteenth embodiments of the present invention,respectively.

FIG. 26 is a plan view showing a semiconductor device manufacturedaccording to a method of designing a semiconductor device in aseventeenth embodiment of the present invention.

FIGS. 27 to 30 are plan views showing variations of the semiconductordevice shown in FIG. 26.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings.

First Embodiment

Referring to FIGS. 1 and 2, a semiconductor device according to a firstembodiment of the present invention includes a semiconductor substrate 1having a main surface 1 a, a plurality of interconnections 11 formed ina capacitance forming region 22 on main surface 1 a, a plurality ofinterconnections 12 formed outside of capacitance forming region 22, andan insulating layer 5 formed on main surface 1 a and filling in betweeneach of interconnections 11 and 12. Interconnections 11 and 12 areformed for example of a metal such as copper (Cu) or aluminum (Al),polysilicon, or the like. Insulating layer 5 is formed for example ofTEOS (tetra ethyl ortho silicate), BPTEOS, FSG (F-doped silicate glass),or a silicon oxide film or a silicon nitride film doped with apredetermined concentration of phosphorus (P) or boron (B).

In p-type semiconductor substrate 1, a p well 2 is formed with apredetermined depth from main surface 1 a. In main surface 1 a ofsemiconductor substrate 1, an isolating oxide film 3 is formed in p well2. Further, in main surface 1 a, an active region 4 connected to aground potential is formed with a predetermined depth on either side ofisolating oxide film 3. Isolating oxide film 3 extends below capacitanceforming region 22 in which the plurality of interconnections 11 areformed, and active region 4 extends below the plurality ofinterconnections 12.

Interconnections 11 and 12 are formed in a plane 21 extending parallelto main surface 1 a at a position apart from main surface 1 a. Aplurality of planes 21 are defined at equal intervals (hereinafter,layers in which the plurality of planes 21 are defined will be referredto as an M (metal) 1 layer, an M2 layer, an M3 layer, respectively, inorder of closeness to main surface 1 a, a space between main surface 1 aand M1 layer will be referred to as a CT (contact) layer, and spacesbetween vertically adjacent M layers will be referred to as a V (viahole) 1 layer, a V2 layer, a V3 layer, respectively). Interconnections11 and 12 are formed in each of M1 layer to M4 layer such that, whenmain surface 1 a is viewed from the front of FIG. 2, they are seenoverlying each other on main surface 1 a.

Each of the plurality of interconnections 11 extends in plane 21 in apredetermined direction (a direction shown by an arrow 23 in FIG. 2).The plurality of interconnections 11 align each other at equal intervalsin a direction orthogonal to the direction in which interconnections 11extend (a direction shown by an arrow 24 in FIG. 2).

In plane 21, interconnections 15 and 16 are formed apart from each otherto extend in the direction shown by arrow 24, between active regions 4formed on both sides of isolating oxide film 3. The plurality ofinterconnections 11 include a plurality of interconnections 11 nbranched from interconnection 15 and extending toward interconnection16, and a plurality of interconnections 11 m branched frominterconnection 16 and extending toward interconnection 15.Interconnections 11 m and 11 n are arranged in such a manner that theteeth of two combs face each other in an interdigitated pattern.

Each of the plurality of interconnections 12 extends in plane 21 in thesame direction as the direction in which the plurality ofinterconnections 11 extend. The plurality of interconnections 12 areformed adjacent to interconnections 11 p of the plurality ofinterconnections 11 located at the edges of capacitance forming region22. That is, the plurality of interconnections 12 are positioned at bothends of the plurality of interconnections 11 in the direction in whichinterconnections 11 align. The distance between interconnection 11 p andinterconnection 12 is the same as the distance between neighboringinterconnections 11.

Referring to FIGS. 1 to 4, interconnections 11 and 12 in verticallyadjacent layers are connected by via holes 14 and 13, respectively,formed in V1 layer to V3 layer. Note that, in FIG. 2, via holes 14 and13 formed in V3 layer are shown by dashed lines. Further,interconnection 12 formed in M1 layer and active region 4 formed in mainsurface 1 a are connected by a contact 10 formed in CT layer.Interconnections 15 and 16 in vertically adjacent layers are connectedby via holes 17 formed in V1 layer to V3 layer.

With the configuration described above, the plurality ofinterconnections 11 m are at the same potential, having a potentialdrawn from a predetermined position of interconnection 16 in M4 layer,and the plurality of interconnections 11 n are at the same potential,having a potential drawn from a predetermined position ofinterconnection 15 in M4 layer. Thus, by providing a potentialdifference between interconnections 11 m and 11 n, an interconnectioncapacitance 8 using insulating layer 5 as a dielectric layer is formedbetween interconnections 11 m and 11 n adjacent to each other in eachplane 21 defined in M1 layer to M4 layer. Although a large number ofinterconnections 11 are formed, interconnections 11 m and 11 n can beset at respective predetermined potentials all at once by arranging themin the form of two combs.

In this case, by forming the plurality of interconnections 11 in theplurality of planes 21, interconnection capacitance 8 having a greatercapacitance value can be formed in a limited region on main surface 1 a.Further, since the plurality of interconnections 11 are arranged toalign in the direction orthogonal to their extending direction, thedistance between which interconnections 11 are adjacent to each other inthat direction can be set longer, achieving a greater capacitance value.

Furthermore, since the plurality of interconnections 12 are connectedvia active regions 4 to p well 2 at a ground potential, they are fixedat the ground potential. Thus, the plurality of interconnections 12 actas a shield for capacitance forming region 22, playing a role to blockelectrical interference (noise) from an external circuit provided aroundcapacitance forming region 22. In this case, since the plurality ofinterconnections 12 are arranged at the both ends of the plurality ofinterconnections 11, noise from the external circuit provided on eitherside of capacitance forming region 22 can surely be blocked.

Note that, in FIG. 1, parasitic capacitances 6 formed between mainsurface 1 a of semiconductor substrate 1 and the plurality ofinterconnections 11 provided in M1 layer, and parasitic capacitances 7formed between the plurality of interconnections 11 p and the pluralityof interconnections 12 are shown by dotted lines.

As described above, the semiconductor device in the first embodiment ofthe present invention includes semiconductor substrate 1 having mainsurface 1 a; a plurality of interconnections 11 as firstinterconnections formed in capacitance forming region 22 defined on mainsurface 1 a and extending in a predetermined direction; insulating layer5 formed on main surface 1 a and filling in between each of theplurality of interconnections 11; and a plurality of interconnections 12as second interconnections adjacent to interconnections 11 p as thefirst interconnections arranged at the edges of capacitance formingregion 22, extending in a predetermined direction, and having a fixedpotential. Interconnections 111 and 12 are arranged at substantiallyequal intervals in plane 21 as a first plane parallel to main surface 1a.

Interconnections 11 and 12 are arranged to align in a directionsubstantially perpendicular to the predetermined direction. Theplurality of interconnections 12 are provided at both ends of theplurality of interconnections 11 arranged in plane 21. Interconnections11 and 12 are formed in a plurality of planes 21 spaced with each other.

Although the description has been given in the present embodiment on thecase where the plurality of interconnections 12 are fixed at a groundpotential, the plurality of interconnections 12 may be fixed for exampleat a power supply potential, depending on the type of the well at thebottom. Further, although the description has been given on the casewhere the plurality of planes 21 are defined at equal intervals witheach other, for example the distance between M1 layer and M2 layer maybe different from the distance between M2 layer and M3 layer.Furthermore, although the description has been given on the case whereinterconnections 11 and 12 are formed in four layers from M1 layer to M4layer, it is satisfactory if interconnections 11 and 12 are formed inone or more layers.

Further, when main surface 1 a of p-type semiconductor substrate 1 isprovided with a p well for example, the p well may be fixed at a groundpotential, and when main surface 1 a is provided with an n well, the nwell may be fixed at a power supply potential and semiconductorsubstrate 1 may be fixed at a ground potential. Furthermore, when mainsurface 1 a of n-type semiconductor substrate 1 is provided with an nwell, the n well may be fixed at a power supply potential, and when mainsurface 1 a is provided with a p well, the p well may be fixed at aground potential and semiconductor substrate 1 may be fixed at a powersupply potential.

According to the semiconductor device with the configuration describedabove, the plurality of interconnections 11 constituting interconnectioncapacitance 8 and the plurality of interconnections 12 acting as ashield are formed at equal intervals. Thus, uneven arrangement of theinterconnections will not be caused between the central portion and theend portion of capacitance forming region 22 in plane 21. Therefore,when forming interconnections 11 and 12, etching progresses at a uniformrate anywhere in capacitance forming region 22, ensuring a uniformfinished configuration. Further, since the plurality of interconnections12 are at a fixed potential, the influence of noise from an externalcircuit exerted on interconnection capacitance 8 can be reduced. Thatis, in the present embodiment, the plurality of interconnections 12serve as a dummy element allowing for a uniform process and also as ashield for blocking external noise. For the reasons described above,interconnection capacitance 8 having no fluctuations in a capacitancevalue and offering a desired characteristic can be formed.

Second Embodiment

A semiconductor device in a second embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the first embodiment. Hereinafter, description of identicalparts will not be repeated.

Of FIGS. 5 to 7 showing the semiconductor device of the presentembodiment, the cross section along the line IV-IV in FIG. 6 has aconfiguration identical to that of the cross section shown in FIG. 4. InFIG. 6, via holes 13 formed in V3 layer are shown by dashed lines.

Referring to FIGS. 5 to 7, in the present embodiment; the plurality ofinterconnections 11 in vertically adjacent layers are not connected by avia hole, and insulating layer 5 is filled therebetween. The pluralityof interconnections 11 are formed such that, when main surface 1 a isviewed from the front of FIG. 6, interconnections 11 formed in M1 layerand M3 layer are seen overlying each other on main surface 1 a, andinterconnections 11 formed in M2 layer and M4 layer are seen overlyingeach other on main surface 1 a.

For example, when a cross section along the line VII-VII in FIG. 6 isviewed in FIG. 7, M1 layer and M3 layer are provided withinterconnections 11 m branched from interconnection 16 formed in eachlayer and extending toward interconnection 15. M2 layer and M4 layer areprovided with interconnections 11 n branched from interconnection 15formed in each layer and extending toward interconnection 16. That is,in the present embodiment, interconnections 11 m and 11 n are arrangedin such a manner that the teeth of two combs face each other in aninterdigitated pattern in plane 21 as well as in a plane orthogonal toplane 21.

With this configuration, in the present embodiment, an interconnectioncapacitance 8 a is formed between interconnections 11 m and 11 nadjacent to each other in plane 21, and an interconnection capacitance 8b is also formed between interconnections 11 m and 11 n in verticallyadjacent layers.

According to the semiconductor device with such a configuration, theeffect similar to that described in the first embodiment can beobtained. In addition, since a capacitance is also formed between theinterconnections in vertically adjacent layers, a greater capacitancevalue can be achieved in a limited region on main surface 1 a.

Third Embodiment

A semiconductor device in a third embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the first embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 8, semiconductor substrate 1 of the present embodimentincludes an n well 34 formed on either side of p well 2. P well 2 isformed to be located immediately below interconnections 11 and 12 in alateral direction and a depth direction of the plane of FIG. 8. Insemiconductor substrate 1, an n⁺ well 31 is formed at a predetermineddepth from main surface 1 a. N⁺ well 31 is formed all over the positionunderlying n wells 34 and p well 2 in the lateral direction and thedepth direction of the plane of FIG. 8. N⁺ well 31 extends parallel to nwells 34 and p well 2.

When p well 2 is not used to fix the plurality of interconnections 12 ata potential, p well 2 is only necessary to underlie at least a regionover which, when viewed from above, capacitance forming region 22 isseen on main surface 1 a in the lateral direction and the depthdirection of the plane of FIG. 8. Similarly, n⁺ well 31 is onlynecessary to underlie at least all the region over which, when viewedfrom above, capacitance forming region 22 is seen on main surface 1 a.

In main surface 1 a, isolating oxide film 3 is formed at a boundarybetween n well 34 and p well 2, and active region 4 is further formed onn well 34. Active region 4 is connected via contact 10 to aninterconnection 33 formed on main surface 1 a and fixed at a powersupply potential. With this configuration, n⁺ well 31 is fixed at thepower supply potential.

According to the semiconductor device with such a configuration, theeffect similar to that described in the first embodiment can beobtained. In addition, by providing semiconductor substrate 1 with n⁺well 31 having a fixed potential, noise transmitted mainly from a rearside of semiconductor substrate 1 to capacitance forming region 22 canbe blocked effectively. The effect similar to that obtained by n⁺ well31 can also be achieved by p well 2 having a fixed potential.

It is to be noted that application is not limited to the potentialfixing described in the present embodiment. When an n well is formed inmain surface 1 a of semiconductor substrate 1 and a p⁺ well is formedunder the n well, the plurality of interconnections 12 may be fixed at apower supply potential via the n well and the p⁺ well may be fixed at aground potential. Thus, the effect similar to that described above canbe obtained.

Fourth Embodiment

A semiconductor device in a fourth embodiment of the present inventionshown in FIGS. 9 to 12 basically has a configuration similar to those ofthe semiconductor devices in the first and the third embodiments.Hereinafter, description of identical parts will not be repeated.

In FIG. 10, via hole 13 formed in V4 layer is shown by a dashed line.

Referring to FIGS. 9 to 12, in the present embodiment, a plane 37extending parallel to main surface 1 a is defined at a position of an M5layer spaced from M4 layer by a predetermined interval therebetween.Plane 37 is defined such that capacitance forming region 22 is locatedbetween plane 37 and main surface 1 a. Plane 37 is provided with aplurality of interconnections 38. The plurality of interconnections 38extend in plane 37 in a direction identical to the direction in whichthe plurality of interconnections 11 extend (a direction shown by arrow23 in FIG. 10). The plurality of interconnections 38 align each other atequal intervals in a direction orthogonal to the direction in whichinterconnections 38 extend (a direction shown by arrow 24 in FIG. 10).

In plane 37, interconnections 41 and 42 are formed apart from each otherto extend in the direction shown by arrow 24. The plurality ofinterconnections 38 include a plurality of interconnections 38 nbranched from interconnection 41 and extending toward interconnection42, and a plurality of interconnections 38 m branched frominterconnection 42 and extending toward interconnection 41, andinterconnections 38 m and 38 n are arranged in such a manner that theteeth of two combs face each other in an interdigitated pattern.Interconnections 38 m and 38 n are formed such that, when main surface 1a is viewed from the front of FIG. 10, they are seen in overlyingrelation with interconnections 11 m, 11 n and interconnections 12 onmain surface 1 a.

Interconnection 12 formed in M4 layer and interconnection 38 formed inM5 layer above interconnection 12 are connected by via hole 13. Withthis configuration, interconnections 12 and 38 are fixed at a groundpotential.

It is to be noted that, in FIG. 9, a parasitic capacitance 39 formedbetween interconnection 38 in M5 layer and interconnection 11 in M4layer is shown by a dotted line.

According to the semiconductor device with such a configuration, theeffect similar to those described in the first and the third embodimentscan be obtained. In addition, since the plurality of interconnections 38covering capacitance forming region 22 from above act as a shieldtogether with the plurality of interconnections 12, noise from anexternal circuit can be blocked further reliably.

Fifth Embodiment

A semiconductor device in a fifth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 13, in the present embodiment, interconnections lplocated at a position adjacent to the plurality of interconnections 12having a fixed potential (i.e., at a position surrounded by a chaindouble-dashed line 46) are connected to a low impedance node. Morespecifically, the plurality of interconnections 11 m includinginterconnections 11 p in FIG. 13 are connected to a relatively lowimpedance node, and the plurality of interconnections 1 in not includinginterconnections 11 p are connected to a relatively high impedance node.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, since the plurality of interconnections lp areconnected to a relatively low impedance node, the influence of parasiticcapacitance 7 formed between interconnection 11 p and interconnection 12can be reduced. Thus, a circuit using interconnection capacitance 8 canbe implemented with higher accuracy, preventing parasitic capacitance 7from causing deviation of a capacitance value ratio in interconnectioncapacitance 8 or deviation from a desired transmissibility wheninterconnection capacitance 8 is utilized in an integrator using anamplifier.

Sixth Embodiment

A semiconductor device in a sixth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 14, in the present embodiment, interconnections 38formed in M5 layer and connected by via holes 13 to interconnections 12having a fixed potential and interconnections 11 m formed in M5 layerand connected by via holes 14 to interconnections 11 m formed in M4layer are provided in an interdigitated pattern. Further, the pluralityof interconnections 11 m include interconnections 11 p formed at aposition adjacent to the plurality of interconnections 12 having a fixedpotential (i.e., at a position surrounded by a chain double-dashed line51). The plurality of interconnections 11 m are connected to arelatively low impedance node, and the plurality of interconnections 11n are connected to a relatively high impedance node.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, interconnections 38 having a fixed potential canbe used as a shield for capacitance forming region 22, and the influencedue to parasitic capacitance 7 can also be reduced as in the effectdescribed in the fifth embodiment.

Seventh Embodiment

A semiconductor device in a seventh embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 15, in the present embodiment, a plurality of floatinginterconnections 57 spaced from each other are formed at a position inM4 layer sandwiched between interconnections 12 at both ends (i.e., at aposition surrounded by a chain double-dashed line 56). The plurality offloating interconnections 57 extend in a depth direction of the plane ofFIG. 15. Floating interconnection 57 is completely surrounded byinsulating layer 5, and has a floating potential. More specifically,floating interconnection 57 at a floating potential is positionedbetween interconnection 38 formed in M5 layer and having a fixedpotential and interconnection 11 formed in M3 layer.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, by providing floating interconnection 57 having afloating potential at the position described above, parasiticcapacitance 39 formed between interconnection 11 and interconnection 38(see FIG. 9) can be reduced. Thus, a circuit using interconnectioncapacitance 8 can be implemented with higher accuracy.

Eighth Embodiment

A semiconductor device in an eighth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 16, in the present embodiment, a plurality of floatinginterconnections 59 spaced from each other are formed at a position inM1 layer sandwiched between interconnections 12 at both ends (i.e., at aposition surrounded by a chain double-dashed line 58). The plurality offloating interconnections 59 extend in a depth direction of the plane ofFIG. 16. Floating interconnection 59 is completely surrounded byinsulating layer 5, and has a floating potential. More specifically,floating interconnection 59 at a floating potential is positionedbetween interconnection 11 formed in M2 layer and main surface 1 a ofsemiconductor substrate 1.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, by providing floating interconnection 59 having afloating potential at the position described above, parasiticcapacitance 6 formed between interconnection 11 and main surface 1 a(see FIG. 9) can be reduced. Thus, a circuit using interconnectioncapacitance 8 can be implemented with higher accuracy.

Ninth Embodiment

A semiconductor device in a ninth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 17, in the present embodiment, a plurality of floatinginterconnections 61 are formed at a position adjacent to the pluralityof interconnections 12 in M1 layer to M4 layer (i.e., at a positionsurrounded by a chain double-dashed line 60). The plurality of floatinginterconnections 61 extend in a depth direction of the plane of FIG. 17.Floating interconnection 61 is completely surrounded by insulating layer5, and has a floating potential. More specifically, floatinginterconnection 61 at a floating potential is positioned betweeninterconnection 11 p formed in each of M1 to M4 layers andinterconnection 12 having a fixed potential.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, by providing floating interconnection 61 having afloating potential at the position described above, parasiticcapacitance 7 formed between interconnection 11 and interconnection 12(see FIG. 9) can be reduced. Thus, a circuit using interconnectioncapacitance 8 can be implemented with higher accuracy.

Tenth Embodiment

A semiconductor device in a tenth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 18, in the present embodiment, no interconnections areprovided in a position in M4 layer sandwiched between interconnections12 at both ends (i.e., at a position surrounded by a chain double-dashedline 63), and the position is filled with insulating layer 5. Thus, thedistance from interconnection 38 formed in M5 layer to interconnection11 adjacent to interconnection 38 (i.e., interconnection 11 formed in M3layer) is greater than the distance between vertically adjacentinterconnections 11.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, by providing no interconnections in M4 layer andincreasing the distance between interconnection 11 and interconnection38, parasitic capacitance 39 formed between interconnection 11 andinterconnection 38 (see FIG. 9) can be reduced. Thus, a circuit usinginterconnection capacitance 8 can be implemented with higher accuracy.

Eleventh Embodiment

A semiconductor device in an eleventh embodiment of the presentinvention basically has a configuration similar to that of thesemiconductor device in the seventh embodiment. Hereinafter, descriptionof identical parts will not be repeated.

Referring to FIG. 19, in the present embodiment, a plurality of floatinginterconnections 57 are formed at a position in M4 layer sandwichedbetween interconnections 12 at both ends, corresponding to every otherinterconnection 11 therebelow. The plurality of floatinginterconnections 57 are not provided at a portion in which a parasiticcapacitance may lead to deterioration of circuit accuracy (i.e., aportion to be a high impedance node when a circuit is implemented), andprovided at a portion to be a low impedance node.

According to the semiconductor device with such a configuration,deterioration of accuracy in a high impedance node due to a parasiticcapacitance can further be reduced as compared to the semiconductordevice in the seventh embodiment. Furthermore, even in M4 layer in whichfloating interconnections 57 are thinned out compared to the case ofFIG. 15, the area occupied by the interconnections is larger than in thecase shown in FIG. 18, enabling to form more planar M5 layer on M4layer.

Twelfth Embodiment

A semiconductor device in a twelfth embodiment of the present inventionbasically has a configuration similar to that of the semiconductordevice in the fourth embodiment. Hereinafter, description of identicalparts will not be repeated.

Referring to FIG. 20, in the present embodiment, no interconnections areprovided in a position in M1 layer sandwiched between interconnections12 at both ends (i.e., at a position surrounded by a chain double-dashedline 66), and the position is filled with insulating layer 5. Thus, thedistance from main surface 1 a of semiconductor substrate 1 tointerconnection 11 adjacent to main surface 1 a (i.e., interconnection11 formed in M2 layer) is greater than the distance between verticallyadjacent interconnections 11.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, by providing no interconnections in M1 layer andincreasing the distance between interconnection 11 and main surface 1 a,parasitic capacitance 6 formed between interconnection 11 and mainsurface 1 a (see FIG. 9) can be reduced. Thus, a circuit usinginterconnection capacitance 8 can be implemented with higher accuracy.

Thirteenth Embodiment

A semiconductor device in a thirteenth embodiment of the presentinvention basically has a configuration similar to that of thesemiconductor device in the eighth embodiment. Hereinafter, descriptionof identical parts will not be repeated.

Referring to FIG. 21, in the present embodiment, a plurality of floatinginterconnections 59 are formed at a position in M1 layer sandwichedbetween interconnections 12 at both ends, corresponding to every otherinterconnection 11 therebelow. Floating interconnections 59 are notprovided at a portion in which a parasitic capacitance may lead todeterioration of circuit accuracy (i.e., a portion to be a highimpedance node when a circuit is implemented), and provided at a portionto be a low impedance node.

According to the semiconductor device with such a configuration,deterioration of accuracy in a high impedance node due to a parasiticcapacitance can further be reduced as compared to the semiconductordevice in the eighth embodiment. Furthermore, even in M1 layer in whichfloating interconnections 59 are thinned out compared to the case ofFIG. 16, the area occupied by the interconnections is larger than in thecase shown in FIG. 20, enabling to form more planar M2 layer on M1layer.

Fourteenth Embodiment

A semiconductor device in a fourteenth embodiment of the presentinvention basically has a configuration similar to that of thesemiconductor device in the fourth embodiment. Hereinafter, descriptionof identical parts will not be repeated.

In FIG. 23, via hole 13 formed in V4 layer is shown by a dashed line.Referring to FIGS. 22 and 23, in the present embodiment, the area ratioof active region 4 to a region 71 on main surface 1 a immediately abovewhich interconnections 111 and 12 are formed satisfies a predeterminedoccupied area ratio.

Here, a “predetermined occupied area ratio” refers to an area ratio of aspecific region defined to produce planar main surface 1 a through themanufacturing process of a semiconductor device (including an activeregion formed by introducing impurities into main surface 1 a, and aregion in which a polysilicon film is formed in contact with mainsurface 1 a). The predetermined occupied area ratio is, for example, notless than 25%, not less than 50%, or not less than 75%.

The semiconductor device in the fourteenth embodiment of the presentinvention includes active region 4 as the specific region defined inmain surface 1 a. The area ratio of active region 4 to region 71 on mainsurface 1 a immediately above which interconnections 11 and 12 areformed is not less than a predetermined value.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourth embodiment can beobtained. In addition, since active region 4 is formed to satisfy apredetermined occupied area ratio, a planar film (insulating layer 5 inthe present embodiment) can be formed on main surface 1 a. Accordingly,interconnections 11 and 12 can be formed on the planar film, and thusinterconnections 11 and 12 can be finished in a more uniformconfiguration.

Fifteenth Embodiment

A semiconductor device in a fifteenth embodiment of the presentinvention basically has a configuration similar to that of thesemiconductor device in the fourteenth embodiment. Hereinafter,description of identical parts will not be repeated.

Referring to FIG. 24, in the present embodiment, isolating oxide film 3is additionally formed at a position in main surface 1 a in which activeregion 4 has been formed in FIG. 22. Isolating oxide film 3 is locatedimmediately below interconnection 11 n having relatively high impedance.In contrast, active region 4 is located immediately belowinterconnection 11 m having relatively low impedance.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fourteenth embodiment can beobtained. In addition, the influence of parasitic capacitance 6 formedbetween main surface 1 a and interconnection 11 n connected to a highimpedance node can be reduced.

Sixteenth Embodiment

A semiconductor device in a sixteenth embodiment of the presentinvention basically has a configuration similar to that of thesemiconductor device in the fifteenth embodiment. Hereinafter,description of identical parts will not be repeated.

Referring to FIG. 25, in the present embodiment, a polysilicon film 73is formed immediately below interconnection 11 m having relatively lowimpedance, and isolating oxide film 3 is formed immediately belowinterconnection 11 n having relatively high impedance.

According to the semiconductor device with such a configuration, theeffect similar to that described in the fifteenth embodiment can also beobtained.

Seventeenth Embodiment

Referring to FIG. 26, a semiconductor device 83 according to aseventeenth embodiment of the present invention has a configuration inwhich drawing terminal cells 80 and 81 and a unit capacitance cell 82located between drawing terminal cells 80 and 81 are combined in a Ydirection. Drawing terminal cells 80 and 81 include the interconnectionconfiguration of interconnections 41 and 42 in the semiconductor deviceshown in FIG. 10, and unit capacitance cell 82 includes theinterconnection configuration having a predetermined width betweeninterconnection 41 and interconnection 42. The length of drawingterminal cells 80 and 81 and unit capacitance cell 82 in an X directionis determined to satisfy the predetermined occupied area ratio describedin the fourteenth embodiment.

FIGS. 27 to 30 show variations of the semiconductor device in FIG. 26.Referring to FIG. 27, a semiconductor device 84 has a configuration inwhich drawing terminal cells 80 and 81 and two unit capacitance cells 82located between drawing terminal cells 80 and 81 are combined in the Ydirection. Referring to FIG. 28, a semiconductor device 85 has aconfiguration in which drawing terminal cells 80 and 81 and 10 unitcapacitance cells 82 located between drawing terminal cells 80 and 81are combined in the Y direction.

Referring to FIG. 29, a semiconductor device 86 has a configuration inwhich four semiconductor devices 85 shown in FIG. 28 are connected inparallel, and a polysilicon layer 87 extending in a band shape islocated on its either side. Polysilicon layer 87 is provided toguarantee a sufficient occupied area ratio in such a case where there isno gate layer in the periphery of the capacitance forming region.

Referring to FIG. 30, a semiconductor device 90 has a configurationsubstantially similar to that of semiconductor device 86 in FIG. 29,except that two polysilicon layers 88, extending in a band shape anddivided in the middle, are located on its either side. Polysiliconlayers 88 divided to have an appropriate size are used when polysiliconlayer 87 shown in FIG. 29 would provide too high an occupied area ratio.

A method of designing the semiconductor device in the seventeenthembodiment of the present invention utilizes the semiconductor devicesdescribed in the fourteenth to the sixteenth embodiments. The method ofdesigning the semiconductor device includes the steps of unitizing thesemiconductor device as a unit capacitance cell, and combining aplurality of such unit capacitance cells.

According to the method of designing the semiconductor device with sucha configuration, since the cells satisfying a predetermined occupiedarea ratio are combined to determine the configuration of thesemiconductor device, the semiconductor device also always satisfies thepredetermined occupied area ratio as a whole. This makes it possible todesign a semiconductor device satisfying a predetermined occupied arearatio without going through a complicated design process. With thismethod, a semiconductor device having an interconnection capacitancewith small fluctuations during processing can be obtained.

The embodiments described above may be combined as appropriate to formthe semiconductor device in accordance with the present invention, andin that case, the effects similar to those described in the combinedembodiments can be obtained. For example, when the configurationsatisfying the occupied area ratio shown in FIG. 22 is applied to thesemiconductor device shown in FIG. 13, the effects described in thefifth and the fourteenth embodiments can be achieved.

According to the present invention, a semiconductor device having acapacitive element for which external electrical interference issufficiently reduced and offering a desired characteristic can beprovided.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A semiconductor device, comprising: a semiconductor substrateincluding a main surface; a plurality of first interconnections formedin a capacitance forming region defined on said main surface andextending in a predetermined direction; a plurality of secondinterconnections each adjacent to one of said plurality of firstinterconnections located at an edge of said capacitance forming region,extending in said predetermined direction, and having a fixed potential;and an insulating layer formed on said main surface and filling inbetween each of said plurality of first interconnections and betweensaid first interconnection and said second interconnection adjacent toeach other, said plurality of first interconnections and said pluralityof second interconnections being located at substantially equalintervals in a first plane parallel to said main surface, and located toalign in a direction substantially perpendicular to said predetermineddirection.
 2. The semiconductor device according to claim 1, whereinsaid plurality of second interconnections are formed at both ends ofsaid plurality of first interconnections located in said first plane. 3.The semiconductor device according to claim 1, wherein said plurality offirst interconnections and said plurality of second interconnections areformed in a plurality of said first planes spaced apart from each other.4. The semiconductor device according to claim 3, wherein said pluralityof first interconnections include a first interconnection located suchthat a distance from said main surface to said first interconnectionadjacent to said main surface is greater than a distance between saidplurality of first planes.
 5. The semiconductor device according toclaim 1, further comprising a floating interconnection located in atleast one of a position between said first interconnection and said mainsurface and a position between said first interconnection and saidsecond interconnection, extending in said predetermined direction, andhaving a floating potential.
 6. The semiconductor device according toclaim 1, further comprising a plurality of third interconnections spacedapart from each other in a second plane parallel to said main surfaceand extending in said predetermined direction, wherein said capacitanceforming region is located between said second plane and said mainsurface.
 7. The semiconductor device according to claim 6, furthercomprising a floating interconnection located between said firstinterconnection and said third interconnection, extending in saidpredetermined direction, and having a floating potential.
 8. Thesemiconductor device according to claim 6, wherein said plurality offirst interconnections and said plurality of second interconnections areformed in a plurality of said first planes spaced apart from each other,and said plurality of first interconnections include a firstinterconnection located such that a distance from said second plane tosaid first interconnection adjacent to said second plane is greater thana distance between said plurality of first planes.
 9. The semiconductordevice according to claim 1, wherein said semiconductor substrateincludes a first well layer of a first conductivity type extending insaid main surface and having said second interconnection electricallyconnected thereto, said first well layer being fixed at one of a groundpotential and a power supply potential.
 10. The semiconductor deviceaccording to claim 9, wherein said semiconductor substrate furtherincludes a second well layer of a second conductivity type extendingparallel to said first well layer at a position immediately below saidcapacitance forming region and apart from said main surface, said secondwell layer being fixed at a potential different from the one of theground potential and the power supply potential at which said first welllayer is fixed.
 11. The semiconductor device according to claim 1,wherein the one of said plurality of first interconnections located atthe edge of said capacitance forming region has impedance lower thanthat of another one of said plurality of first interconnections.
 12. Thesemiconductor device according to claim 1, wherein said semiconductorsubstrate includes a specific region defined in said main surface, andan area ratio of said specific region to a region of said main surfaceimmediately above which said plurality of first interconnections andsaid plurality of second interconnections are formed is not less than apredetermined value.
 13. The semiconductor device according to claim 12,wherein said specific region is located immediately below one of saidplurality of first interconnections having relatively low impedance, andaway from immediately below another one of said plurality of firstinterconnections having relatively high impedance.
 14. The semiconductordevice according to claim 1, wherein said plurality of firstinterconnections are arranged to form teeth of one comb extending froman interconnection fixed at a first potential in one direction and teethof another comb extending from another interconnection fixed at a secondpotential in a direction opposite to the direction in which the teeth ofsaid one comb extend, with the teeth of said one comb and the teeth ofsaid other comb facing each other in an interdigitated pattern.